Should I put my son's father on child support?

My 2 years old was planned. We both had 1 previous child before. We did not get married before having our son. I was crazy in love and believed that marriage was overrated. At 8 months pregnant, I received a letter in the mail from his baby mom stating that she just had another child for him. BTW, I did not know that they were still having sex. He told me that they broke up 5 years ago. Our sons are 3 months apart in age. At first, he used to help with 50% of my son's tuition($300 per month). When my son was younger, he didn't pick him up. In 2017, he gave me $400 for the entire year. For this year, nothing as yet. He picks up our son twice for the month and it's never planned just random. Whenever I ask for financial help, he tells me that he didn't have it because he is the only one taking care of the other 2 kids.